
uniform mat4 ViewMatrix;
uniform mat4 ViewMatrixInverse;
uniform mat4 ViewProjectionMatrix;

/* ---- Instantiated Attribs ---- */
in vec3 pos;

/* ---- Per instance Attribs ---- */
/* Assumed to be in world coordinate already. */
in vec4 headSphere;
in vec4 tailSphere;
in vec3 xAxis;
in vec3 stateColor;
in vec3 boneColor;

flat out vec3 finalStateColor;
flat out vec3 finalBoneColor;
out vec3 normalView;

void main()
{
	vec3 bone_vec = tailSphere.xyz - headSphere.xyz;
	float bone_len = max(1e-8, sqrt(dot(bone_vec, bone_vec)));
	float bone_lenrcp = 1.0 / bone_len;
#ifdef SMOOTH_ENVELOPE
	float sinb = (tailSphere.w - headSphere.w) * bone_lenrcp;
#else
	const float sinb = 0.0;
#endif

	vec3 y_axis = bone_vec * bone_lenrcp;
	vec3 z_axis = normalize(cross(xAxis, -y_axis));
	vec3 x_axis = cross(y_axis, z_axis); /* cannot trust xAxis to be orthogonal. */

	vec3 sp, nor;
	nor = sp = pos.xyz;

	/* In bone space */
	bool is_head = (pos.z < -sinb);
	sp   *= (is_head) ? headSphere.w : tailSphere.w;
	sp.z += (is_head) ? 0.0 : bone_len;

	/* Convert to world space */
	mat3 bone_mat = mat3(x_axis, y_axis, z_axis);
	sp = bone_mat * sp.xzy + headSphere.xyz;
	nor = bone_mat * nor.xzy;

	normalView = mat3(ViewMatrix) * nor;

	gl_Position = ViewProjectionMatrix * vec4(sp, 1.0);

	finalStateColor = stateColor;
	finalBoneColor = boneColor;
}
